The present invention relates to a hydraulic pump having a first pump element sucking from a common suction chamber into a first chamber forming the pressure outlet of the hydraulic pump, and a second pump element sucking into a second chamber.
A hydraulic pump of the general type is disclosed in DE-A-3,837,599, but this known pump is too complicated in construction. The present invention has as an object the construction of such a pump type in a structurally simpler fashion and thus the achievement of a more cost-effective production.
The foregoing objective has been achieved with a hydraulic pump in which, with a discharge pressure of the pressure outlet below a first limiting value of a discharge pressure, two pressure chambers are connected to one another via an open unidirectional valve, and the connection between the pressure chambers and the common suction chamber is locked by a shifter; with a discharge pressure at a first limiting value, the delivery valve is closed and the control valve is set in a position in which only the second pressure chamber is connected to the suction chamber; and, with a discharge pressure at a second limiting value corresponding to a position of the control valve, a throttle connection between the first pressure chamber and the second pressure chamber is opened by the actuating piston, and the connection between the second pressure chamber and the suction chamber continues to remain open due to the shifter.
The basic difference in the solution according to the present invention by contrast with the previously known oil pump resides essentially in the fact that, below the first limiting value of a discharge pressure prevailing at the pressure outlet, the flow of the second chamber is discharged directly via the unidirectional valve, i.e. a non-return valve, into the first chamber forming the pressure outlet of the pump. As a result, control valves necessary and control channels connected thereto can be eliminated.
DE-A-3,142,604 discloses an oil pump in which two pump units discharge from a common suction chamber optionally into a common pressure outlet or separate pressure outlets, and have a unidirectional valve connecting the two pressure outlets to one another. This known oil pump arrangement is different from the present invention because the respective unidirectional valves function completely differently. In particular, the unidirectional valve of the present invention ensures that, below a first limiting value of the discharge pressure prevailing at the pressure outlet, the flows of the two pump units are led into a common pressure outlet of the pump, and the unidirectional valve of the known oil pump device is connected and controlled such that it cannot open until it is above a preset discharge pressure at the pressure outlet of the pump, while it is held closed by a control valve in the case of a discharge pressure below this limiting value.
Owing to the different sort of functional designation of that previously known oil pump, in which, by contrast with that according to the present invention, two discharge pumps discharge into a common pressure outlet not in the case of a low discharge pressure at the pump outlet but in the case of a high discharge pressure at the pump outlet, that pump has a control and switching mechanism that is of an entirely different overall sort, as a result of which the structure and the function of the valve controls necessary in the two cases are not comparable to one another.